1. Field of the Invention
The present invention relates to current controlling method and apparatus for an electric rotating machine such as a compound motor.
2. Description of the Related Art
A Japanese Patent Application First Publication No. Heisei 11-356015 published on Dec. 24, 1999 exemplifies a previously proposed rotating machine. The previously proposed rotating machine described in the above-described Japanese Patent Application First Publication adopts a three-layer structure of two rotors and a single stator. When a compound (alternating) current synchronized with rotation speeds of the two rotors is caused to flow through the electric rotating machine so that torques generated on the two rotors are respectively non-interfered with each other.
On the other hand, a compound motor is disclosed in a Japanese Patent Application First Publication No. 2001-231227 published on Aug. 24, 2001 (which corresponds to a U.S. patent application publication Ser. No. US2001/0020805 A1 published on Sep. 13, 2001). The disclosed compound motor has two pairs of stator coils and rotors respectively independently operated of each pair of the stator coils and rotors. In the disclosed compound motor, an ineffectual current in a case where the coils of the same polarities at the two stator coils are connected in parallel to each other is controlled so as to improve an entire working efficiency.